Briggs & Stratton v-twin won't start

[Treewolf]

We have a Grillo Climber with a Briggs & Stratton 8290 v-twin engine, bought new about 7 years ago as far as I recall.

Recently it's required quite a lot of cranking to start and finally doesn't want to start at all.

 

We've drained the fuel and filled with fresh, it cranks well (seems fast to me), there is a good strong spark on both plugs, we've checked that fuel spurts from the pump outlet when cranking, and after a period of cranking there's a smell of fuel and the plugs come out wet with fuel.

The oil level in the sump is normal and the oil doesn't smell of fuel. With the rocker covers off the valves and rockers are spotless and seems to be working as expected. There's nothing I can see to indicate leaking heads but the cranking speed makes me wonder about compression.

 

It now has me baffled and I'd be really grateful for any suggestions for things to check next, if anyone could be kind enough to have any ideas. Thanks.

[spudulike]

I have never had one of these apart but in general, most engine issues of this type are fuel related so pull the carb apart, check that the needle valve is working, check the fuel is flowing in to the carb, check that the float bowl has fuel in it and there is no water or shyte in the bowl. Remove the main jet AND the emulsion tube - this may need coaxing and then ensure all the holes and main jet are clear. Blast some cleaner or brake cleaner through all the holes/channels and reassemble. I am making the assumption that the carb is like the ones fitted to most of the B&S single cylinder engines.

Sometimes the needle jet seals against a tiny rubber O ring and these swell stopping the float being level once the carb is held upside down (Lowering the amount of fuel in the bowl) this can make an engine very lumpy...it did on my Intek engine and can be replaced if you have similar.

One other thing to check is that the choke is sealing fully on a cold engine. This may be operated by a lever, thermal actuator or a throttle position but also worth checking as if the choke isn't sealing, cold starting will be hit and miss. 

[adw]

Leak down test will give you a good idea of the health of the engine internals.

[spudulike]

ADW......I think you mean a compression test...being a four stroke 😉. Not sure if the engine has an automatic decompressor for starting so you may get a low reading if it has.

Much depends on the hours it has done etc, a lot of our diagnosis is done at a glance at the state of the unit. 

[Stubby]

You say it cranks over fast in your opinion . Maybe a valve is stuck open ?  EDIT . Soz . I see you have checked that.

Edited yesterday at 11:11 by Stubby

[Treewolf]

Not sure of the hours but it's been used weekly rather than daily during the mowing season on a single property so will certainly not be excessive hours. I think a compression test will be the next step.

 

It evidently uses pulses of pressure from the crankcase to work the fuel pump, and the pump squirts well when disconnected from the carb. Does this indicate that pistons and rings are sound, or am I overthinking it? Id so it suggests to me any lack of compression is valves or head gasket. As noted the valves are definitely not sticking and the oily ends look pristine but that doesn't mean they're seating.

 

I'm really grateful for the input, thank you. I'm much more familiar with large engines and still learning with this little blighter!

[spudulike]

If you take the plugs out and turn the engine over slowly, you should see the piston rising to top dead centre (TDC) and both tappets on one cylinder rising to fully up so both valves are sealing for the compression leading to power stroke. At this point, make sure there is a small gap under each tappet by moving it up and down feeling for a small amount of play caused by the normal clearance between tappet and valve. If there is no clearance, the tappet needs backing off (the valve seat may also be damaged) or if the gap is massive, you may have a stuck valve.

The fuel pump working wont prove decent compression. A reading of +/- 10 - 15 psi between both cylinders will prove that either both cylinders/pistons are shagged or they are OK. Not sure what reading to expect on mowers but 140+ should be OK on a cold engine.

I would normally check the carb out, if the needle is leaking, it will cause flooding of the engine. 

[adw]

22 hours ago, spudulike said:

ADW......I think you mean a compression test...being a four stroke 😉. Not sure if the engine has an automatic decompressor for starting so you may get a low reading if it has.

Much depends on the hours it has done etc, a lot of our diagnosis is done at a glance at the state of the unit. 

As a Briggs master technician ( I can see your impressed Steve ) you use a leak down tester to check valve leakage, cylinder and piston wear etc. check it out it’s a good bit of kit.

[spudulike]

Ah, I understand your logic now, I thought you were losing it😉

[spudulike]

As a B&S master technician, do you wield a light sabre?👍